Why AO Smith Water Heater Won’t Light [Solved]

Your AO Smith water heater won’t light because of the leading reasons, including a faulty pilot light, an insufficient gas supply, a bad thermocouple, a blocked tube, a defective pressure switch, and so on.

However, before replacing anything, first, try resetting and cleaning your water heater to solve the lighting problems.

Even then, if you struggle to fix it, we have detected each culprit that prevents your heater from igniting and shown their effective solutions.

So, follow our well-proven guide to resolve your lighting problems.

AO smith water heater won't light

AO Smith Water Heater Won’t Light [8 Easy Solutions]

In this section, we will break down every reason your AO Smith water heater won’t ignite and guide you on how to solve them easily. Let’s get started right here.

Note: You can also read how to fix the AO smith water heater won’t stay lit.

1. Gas Supply Issue

An improper gas supply is primarily responsible for not lighting your water heater. Your AO Smith water heater won’t ignite if the unit doesn’t get enough gas supply.

A proper gas supply ensures your water heater lights up. So, without gas, a status light will never stay lit, let alone operate your water heater.

In this case, if the gas valve is in the off position, the unit will receive no gas.

Besides, the light won’t come on if there is any air in the gas supply line and pilot tube. As a result, you can’t expect the pilot to flash or blink.


  • First, make sure the gas valve is in the on position. If it remains in the off position, clock it to the on position to allow the gas supply to the unit.
  • Now, follow the lighting instructions on the heater’s label to light
  • Second, purge the pilot light tube and gas line to bleed the air. To do so, push the control knob and hold it down until the pilot light comes back on or stays lit. You may need to repeat the process until you get a status light on your heater.

2. Faulty Pilot/Igniter

A faulty pilot or igniter is also a responsive factor behind the AO Smith gas water heater, not lighting.

To light up, there is the potential to have sufficient voltage with the piezo igniter. But when the power is fine, but it won’t glow, it warns that the igniter is defective.

Even the water heater won’t heat if the pilot light doesn’t ignite, as it works as a push button igniter.

Sometimes, there may be a buildup of carbon deposits on the pilot that protects the pilot as it doesn’t get enough combustion air.


  • First, make sure the igniter is receiving enough voltage.
  • But, if it gets restricted to the pilot in any way, try your best to clear it out with a stiff brush or compressed air.
  • After clearing it, try to relight it as instructed in the heater’s manual. And if it gets enough voltage but there is no light at all, the ignitor has defected and should be replaced immediately.

3. Electrode Sparking Problem

The AO Smith water heater won’t spark if there is an issue with the spark electrode. This may happen because of a broken or defective electrode or anode rod.

electrode sparking problem

Basically, the spark electrode allows an intermittent high voltage to light the pilot flame. You won’t see any spark there if the electrode or anode rod gets faulty or worn out.

Plus, over time, the pilot light electrode tip may be obstructed by carbon deposits, dirt, and rust that restrict the igniter from releasing the sparks.

So, the pilot light won’t ignite due to a lack of sparks. 


  • Firstly, start your inspection with the wire connections of the igniter and see if the igniter is getting enough voltage. If there are any faulty connections, reconnect them and tighten them up. Hopefully, the tips will solve the issue.
  • If reconnecting the igniter wires fails to get the expected result, turn off the gas valve and remove the access panel to get to the burner assembly and pull it out.
  • Look through the window to determine whether there is a small spark igniter with the burner.
  • Ensure the electrode or pilot light is fully clean and doesn’t get damaged. If not so, you can use emery cloth or a stiff brush to clean any debris from it.
  • Hold and press the piezo igniter to light it. Yet if the igniter can’t produce any spark, then the anode rod has gone badly.
  • If you can’t clean, you have to replace the heater’s faulty electrode and igniter parts as soon as you can.

4. Defective Thermocouple/Thermopile

A faulty thermocouple is another major culprit for your AO Smith water heater not igniting.

Basically, the water heater thermocouple is considered the brain of the water heater.


A thermocouple detects heat on the pilot flame and allows your heater to turn on. But when it gets bad, it shuts off the gas both for the pilot light and the burner.

So, it’s a clear sign to you that the flame can’t heat the thermopile sufficiently.

Besides, the pilot and the burner won’t be able to ignite unless the thermopile reaches its operating temperature.

On the other hand, you will face the following problems due to the bad or broken thermocouple. For Instance;

  • The pilot light is on the AO Smith Water Heater, but the burner stays lit.
  • Once lighted the pilot, but it went out when you released the control knob.
  • The status light won’t come on for 90 seconds after the pilot light operation.

However, let’s know how to solve the problems.


  • To fix it, first, turn off the gas valve and remove the access cover. Let the unit cool down for 10 minutes to cool your thermocouple.
  • Then, locate the thermocouple. Examine it to see if it gets clogged or bad.
  • Pull out the thermocouple with a screwdriver.
  • Ensure the thermocouple has no rust. If it gets rusty, clean it with sandpaper and scrape off the dirt so that the pilot gets enough ventilation.
  • Try to relight the pilot by following the manual lighting instructions on the water heater’s label. If you fail to light it, then replace the thermopile.
  • If these steps for heater thermocouple cleaning can’t solve the issue, there may be a problem with its bent or defection. And it is no longer functional as it won’t be able to sense the heat.
  • But if you notice the thermocouple is bent or bad, it would be best to replace the broken thermocouple.
replace the  thermocouple
  • You can watch the below video on how to replace a thermocouple by yourself.

5. Blocked Pitot Tube

A blocked or dirty pilot tube is also the next reason for having no status light with the AO Smith water heater.

Your water heater won’t ignite because it’s being blocked by dirt, dust, and debris that restricts the flow of gas from the pilot tube.

It ensures a spontaneous flow to the burner and pilot light functionalities.

But when you cannot ignite, as usual, it means that the pilot light is not getting the proper fuel to ignite at all.


When your pilot tube gets dirty, take a long needle and poke it through the pilot hole to clear out debris from there.

Repeat the process as required to remove the dust and debris that has accumulated there.

lighting instructions

To make sure it has been cleaned, try to relight the pilot to see whether the pilot blinks a bright or blue flame. Hopefully, the tips will fix the problem.

6. Defective Gas Valve

When either cleaning the pilot light or replacing the thermocouple doesn’t help ignite your water heater, the issue might be with the defective gas control valve.

This essential part measures the amount and pressure of a gas as needed in the unit and allows the pilot to be lit.

Unfortunately, if the control valve cannot produce the right amount of gas, it won’t allow your heater to heat and stay lit.


  • To solve the issue, just disconnect the gas lines.
  • Then you will need an adjustable wrench to disconnect the lines, such as the pilot tube lines, piezo igniter, thermal switches, and thermocouple with the gas control valve, and remove the dirty gas valve regulator valve with a threaded pipe.
  • Now, install and screw a new gas control valve into your AO water heater, as this part is not a serviceable unit at all.
  • Reconnect the control valve connections and turn on the gas supply.
  • If you aren’t inclined to replace it, call a professional plumber to reinstall it safely.

Note: Be alert. Too much gas flow can cause fires and explosions.

7. Faulty Pressure Switch

A faulty pressure switch is also responsible for the AO electronic water heater pilot light, not lighting.

It works as a safety feature on the heater that detects the negative pressure produced from the draft motor.

faulty pressure switch

When the proper combustion/airflow is received, the switch closes and signals the control board to run the ignition procedures.

But if the pressure switch is defective or faulty, the ignition process will stall and the heater won’t light at all.


To solve the pressure switch issue, don’t forget to measure the voltage using an ohmmeter because a defective switch may leave a high voltage.

For the broken switch, it is wise to replace the malfunctioning pressure switch by installing a new one.

8. Damaged Gas Burner

If all attempts cannot light the heater, it comes to the point of the damaged gas burner. And you can’t expect a light with your AO Smith water heater.

Plus, this may occur because an old water heater or the main burner chamber may have cracked.

Unfortunately, your water heater has reached an extreme old age.


You may have to change the entire burner assembly, as it is quite impossible to repair.

So, it would be wise to replace the gas burner ASAP.

Reset Your AO Smith Water Heater

When you are struggling to ignite your AO Smith water heater, before going to any maintenance or repair, first try resetting it.

Because, as you’ll see, it might solve most of the lighting problems.

So, follow these 6 effective steps to reset your AO Smith water heater.

Step 1: Take your adjustable screws/tools. Go to the electric panel, find the breaker, and flip it to the off position.

Step 3: Remove the screws that hold the cover in place by opening the cover panel.

Step 4: Look for the reset button beneath the metal cover near the center of the unit.

It may be hidden under a protective material (insulation). You’ll get a “Reset” button near the thermostat.

 Step-5: Simply press the reset button. After pressing on it, you’ll hear a ‘click’ sound that shows your heater has been reset to the point.

 Step 6: Return to the electric panel and turn the breaker switch to ON.


What is a water heater pilot light?

A pilot light is an essential flame part of a water heater. It provides a flame to light, including the gas, the main burner, and various heating elements, and produces heat. Finally, your heater runs smoothly.

Does the AO Smith water heater pilot light stay lit all the time?

A gas water heater has a small flame (called a “pilot light”) to ignite the burner. The pilot light ignites the burner to heat the water. So, it is normal to stay light all the time.

Why is my AO Smith water heater pilot light going out repeatedly?

Your pilot light stays on, but it is going out repeatedly due to an imbalance between the gas supply and the air. It requires enough oxygen; otherwise, the pilot can’t operate properly and goes out.


Fortunately, we have already figured out the culprits that are responsible for your AO Smith water heater won’t be light.

So, whenever you face any lighting issues with your AO Smith water heater, the above well-proven guide will definitely be effective for you to solve the issues by yourself.

Yet, if you have questions about the ignition issue, let’s know in your comments. We will reach out to you with a possible solution ASAP.

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